docs: def retrieve(self, request):
          """Look up request in cache, skipping if verb is forbidden.
  
          :param requests.Request request: HTTP request
  
          """
          if request.method not in CACHE_VERBS:
              return
          try:
              response = self.data[request.url]['response']
              logger.info('Retrieved response from cache')
              return response
          except KeyError:
              return None